6. Facebook gets how to monetize mobile through paid advertising without wrecking the user experience. (In Q4 2013 they crossed over from 49% of revenue from mobile to 53% from a base of 945M mobile monthly active users) Source: Facebook, TechCrunch

Why $16B to $19B? I am not a financial analyst, but here are a few thoughts:

- WhatsApp already generates $1/user for a chunk of their users through a subscription fee (less fee to app store?)

- If WhatsApp users can be monetized at the same value, that adds another 50% approximately in mobile ad revenue

- Facebook reported 914 minutes of use on mobile per month in 2013 (Source: allthingsd.com)

- According to Mobidia, only Kakao Talk has more

- WhatsApp is already located in Si Valley

There are a dwindling number of privately held companies with audience numbers in the hundreds of millions. Tencent (WeChat) is public. LINE belongs to Naver Corporation. Rakuten bought Viber last week.